Arbor



March 20, 1962 G. HoHwART ETAL 3,025,737

ARBOR Original Filed Aug. 21, 1957 5 Sheets-Sheet l ,cli

March 20, 1962 G. HoHWART ETAL 3,025,737

ARBOR Original Filed Aug. 21, 1957 3 Sheets-Sheet 2 wauw.

March 20, 1962 Original -Filed Aug. 2l, 195'? G. HOHWART ETAL ARBOR 3 Sheets-Sheet 5 1N VEN TORS eoye Hola/472.

fr rok/vifs 3,025,737 Patented Mar'. 2G, 1952 nce 3,025,737 ARBOR George Hohwart, Farmington Township, Oakland County, and Ernest F. Hollwart, Detroit, Mich., assignors to N. A. Woodworth Company, Ferndale, Mich., a corporation of Michigan Continuation of abandoned application Ser. No. 679,395, Aug. 21, 1957. This application Sept. 4, 1959, Ser. No.

1 Claim. (Cl. 82-44) This invention relates to new and useful improvements in arbor chucks.

This is a continuation of our copending application serial No. 679,395, tiled August 2l, 1957, now abandoned.

The device embodying the instant invention is an outgrowth of the development which led to the expansion arbor disclosed in our application series No. 119,192, tiled October 1, 1949, which matured into Patent No. 2,626,811 on January 27, 1953. The arbor of this invention is used in the same general way and serves the same general function as the expansion arbor but the two arbors have different primary uses. The expansion arbor is a heavy-duty chuck adapted primarily for relatively large workpieces and is pre-eminently suited for gripping such workpieces exceedingly tightly. Also, the expansion arbor is relatively substantially more expensive than the instant device. The latter is adapted primarily for relatively small workpieces, although it can be used, if desired, for larger pieces as well. It is simpler in construction than the expansion arbor and accordingly is less expensive to manufacture. In addition, the device of this invention is superior to the expansion arbor in certain respects in that it accurately chucks a workpiece which is relatively short in length compared to its diameter. While the instant device can be adapted for either internal or external chucking, it is primarily adapted and pre-eminently suited to chuck a workpiece internally, viz., the arbor is inserted into a hole in the workpiece and when so inserted it grips the wall of the hole to hold the workpiece securely and centered properly on the arbor. When so used, the arbor provides a means for checking various physical characteristics of the workpiece and if desired it can be devised to grip the workpiece suiciently tightly so that machining or other operations can -be performed thereon. It is exceedingly difficult to chuck a workpiece in this manner if the hole in which the arbor is used is relatively short compared to its diameter. Such workpieces tend to cock on the arrbor, and this is particularly true if pressure is applied thereto as by machining operations, The instant device is superior to any other chuck within our knowledge for holding workpieces of this type exactly centered,

From the foregoing it will be readily apparent that a important object of the present invention is to provide a chuck that is primarily adapted and pre-eminently suited for relatively small workpieces or for use in environments where a hole to be chuck is relatively short in length as compared to its diameter.

Another object of the invention is to provide an arbor chuck of the above mentioned character that is relatively simple in construction and inexpensive to manufacture.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the drawings forming a part of this specification and wherein like numerals are employed to designate like parts throughout the same;

FIG. l is a side elevational view of an arbor chuck embodying the invention, parts thereof being broken away and shown in section for clearness of illustration;

FIG. 2 is an enlarged view of the portion of FIG. 1 enclosed in the circle 2 and illustrating the manner in which the arbor chucks the workpiece to hold it securely and centered properly on the arbor;

FIG. 3 is a transverse, sectional view taken on the line 3 3 of FIG. 1;

FIG. 4 is a side elevational view of a modified arbor adapted to chuck a two-diameter hole in a workpiece, parts of the arbor being broken away and shown in section for clearness of illustration;

FIG. 5 is a side elevational view showing a modified form of the invention adapted particularly for threaded holes, parts thereof being broken away and shown in section;

FIG. 6 is a longitudinal sectional view of still another modified form of the invention wherein the arbor is adapted to be expanded mechanically and held solidly against the workpiece vto prevent relative movement between the arbor and the workpiece;

FIG. 7 is a longitudinal sectional view showing another mechanically expanded form of the invention adapted primarily for splined holes in a workpiece;

FIG. 8 is a side elevational view showing an arbor chuck embodying the invention operatively associated with and adapted to be mechanically expanded by a power piston, the arbor being shown in elevation and the piston and its adjuncts being shown in section;

FIG. 9 is a fragmentary, enlarged view showing the arbor illustrated in FIG. 8 in longitudinal section.

Considered in certain of its broader aspects the arbor chuck of this invention comprises a tubular body having a plurality of longitudinal slots spaced substantially uniformly around the circumference thereof and circumferentially continuous rigid portions at the ends of the slots. The slots define longitudinally extending radially flexible members therebetween. Because the flexible members are simply a part of the tubular body they are in the free state straight and parallel to the axis of the arbor. In order for the arbor to function as a chuck the flexible members are provided intermediate the ends and at one side thereof with embossrnents having work engaging surfaces disposed concentrically to the axis of the body. In the case of an internal chuck the embossments are on the outer sides of the flexible members and in the case of an external chuck the embossments are on the inner sides of the flexible members. In -both forms the diameter of the body at the work engaging surfaces is different than. the diameter of the workpiece to be chuck by the arbor. More specifically, the diameter of an internal chuck at the embossments is greater than the diameter of the hole to be chucked, and the diameter of an external chuck at the embossments is less than the external diameter of the part to be chucked. Thus, in both cases, there is circumferential interference between the workpiece and the embossments when .the flexible members are in their normal, free or relaxed state. Similarly, there is an interference lit between the embossments and the workpiece as the latter is pressed onto `or into the chuck. Because of the interference t the flexible members are exed or arched to concave the work engaging surfaces as the workpiece is pressed into engagement with said embossments. The flexible members of the internal chuck are concaved inwardly and the fllexible members of the external chuck are concaved outwardly. Because of the concave shape of the flexible members in use, the work engaging surfaces contact the workpiece separately at spaced points and are arched or spaced away from the workpiece intermediate their ends. In the case of an internal arbor, if the bore in the workpiece is longer than the work engaging surfaces of the embossments, the bore is located and contacted by the arbor on the opposite extreme ends of the embossments. On the other hand, if the length of the bore in the workpiece is shorter than the work engaging surfaces of the embossments, the bore is located and contacted by the embossments on the opposite extreme ends of the bore. Because the workpiece must be forced or pressed onto the arbor, the embossments are formed with tapered or beveled lead ends having a sufficient lead angle to guide the workpiece easily onto the embossments. The lead engagement end portions of the embossments extend from the flexible members to the work engaging surfaces of the embossments. In the case of an internal chuck, the diameter of the arbor at the juncture of the lead engagement portions and the exible members is smaller than the minimum diameter of the workpiece to be chucked and the diameter of the arbor at the juncture of the lead engagement portions and the work engaging surfaces of the embossments is larger than the maximum diameter of the workpiece. Pressure is thus concentrated on the workpiece so as to retain the latter Without tilting and precisely coaxial to the arbor. The above structure and mode of operation is true of every form of the invention herein illustrated and described, and it is this unique action of the liexible members when clamping the workpiece that produces the new mode of use and the beneficial results hereinabove described.

Referring first to the form of the invention shown in FIGS. 1 4 it Will be observed that the arbor comprises a tubular body 20 having plugs 22 and 24 disposed in and snugly fitting the ends thereof. Intermediate the ends thereof, the body 20 is formed with an annular series of circumferentially spaced, longitudinal slots 26. As perhaps best shown in FIG. l, the slots 26 are co-extensive and they are sufficiently long to define inherently flexible and resilient member 28 therebetween. Any suitable number of slots 26 may be provided, and the number provided in any particular instance may vary, depending upon the size of the arbor and the function it is intended to perform. Eight slots are shown in the illustration here under consideration, and these slots are uniformly spaced as shown in FIG. 3 so that the eight members 26 are identical and have uniform properties and characteristics. It is significant that the slots 26 terminate substantial distances from the ends of the body 20 so as to leave circumferentially continuous rigid terminal portions 30 and 32 at both ends thereof. These terminal portions have constant size and form, and they maintain the flexible members 28 also normally constant in size and form and in identical, uniform, spatial relation.

Each member 28 is provided on the outer side thereof with an embossment 34. The outer surfaces of the embossments 34 are curved around the center of the arbor as shown in FIG. 3, and inasmuch as the embossments are circumferentially aligned around the arbor they collectively define a raised band or ridge extending entirely around the body 20 at the middle of the exible members 28, which band is interrupted or ntersected by the slots 26. All of the embossments 34 are finished to an exact radial dimension.

In use, the arbor is inserted into the hole of a workpiece such as the one illustrated at 36, for example. The arbor is constructed so that the diameter of the body 20 at the liexible members 28 and at one terminal thereof is less than the diameter of the hole to be chucked but with the diameter of the body at the embossments 3-4 slightly greater than the diameter of the hole. Thus the body z20 is easily insertible into the hole of the workpiece until the embossments 34 engage the workpiece. At that point the arbor must be forced into the hole so that the embossments may enter. Since the embossments are larger in diameter than the hole, the embossments can only enter the hole by exing the members 28 inwardly. The members 28 thus assume a concave or inverted barrel shape, as shown in FIG. 2. Manifestly, the embossments 34 are correspondingly arched so that each embossment engages the workpiece only at spaced points. In between these points the embossments are arched away from the workpiece. FIG. 2 illustrates the action which occurs but it will be appreciated that the condition of the arbor is exaggerated in the drawings to better illustrate the principle upon which the device operates. In actual practice, the middle of the embossments may clear the workpiece by only a few thousands of an inch. However, regardless of the actual dimension, clearance is provided, and the embossments are pressed by the resiliency inherent in the flexed members 28 outwardly against the workpiece at spaced points, and this phenomenon achieves decidedly beneficial results.

The particular relationship existing between the arbor and the workpiece in use is such that the workpiece is absolutely centered on the arbor and is held exactly at right angles to the axis of the arbor. This is true in the case of narrow as well as wide worpieces, -In actual practice, workpieces in which the hole being chucked is approximately one third as long as its diameter are precisely located and positioned by the arbor. Thus the arbor can be used to determine whether the ends of the workpiece are exactly square with the axis of the hole in which the arbor is mounted or in any other capacity where a device of this nature has utility. When the arbor is removed from the workpiece, it automatically and immedaitely resumes its original size and form.

It will be readily apparent that the arbor automatically takes up part tolerances so that the one device will snugly tit any of a number of production parts even though these parts may vary individually within permissible production tolerances. Heretofore, it has been conventional to use a number 0f solid arbors varying in size to check all the parts or to use a long tapered arbor. When the latter expedient is used, the parts stop at various places 'on the taper, depending upon whether, and the extent to which the par is oversize or undersize. This phenomenon decidely affecs the utility of the arbor adversely since the varying position of the piece on the arbor makes it diliicult to perform a checking or other operation on the workpiece when supported by the arbor, and the taper of the arbor itself makes it diicult, if not impossible, to hold the workpiece with the center of the hole being chucked precisely coincidental with the center of the arbor.

In most instances it is desirable to adapt the arbor for use between centers so that the device can be easily mounted on conventional -machines for checking or other operations. To this end the plugs 22 and 24 are provided with precisely located inwardly tapered center holes 38 and 40.

In order to` facilitate handling of the arbor in use, the tubular body 20 preferably is made longer at one side of the slots 26 than at the other and the relatively long portion is made relatively thicker as at 42 for additional strength. yIn the form of the invention here shown by way of illustration the big end of the arbor is formed with a pair of longitudinally spaced raised bands or ridges 44 and 46 which preferably are made integral with the body. The outer surfaces of the ridges 44 and 46 are knurled or otherwise roughened for ease in holding the arbor in use.

The form of the invention shown in FIG. 4 is generally similar to the form of the invention rst described, except that a modified embossment 48 is used having spaced outer surfaces 50 and 52 disposed different radial distances from the center of the arbor and relieved as at 54 therebetween. The arbor is larger in diameter at the supporting surfaces 52 than at the supporting surfaces 50, and the surfaces 52 are disposed remote from the end of the arbor which is inserted into the workpiece. Also, the surfaces 52 are formed with integral, radially extending stops or shoulders 56.

It will be observed that the workpiece 58 is provided with a two-diameter hole, the small portion 60 adapted to engage the surfaces 50 and the larger portion 62 adapted to engage the surfaces 52 of the arbor. The two portions 60 and 62 of the workpiece are relieved as at 64 therebetween.

In use, the arbor is inserted into the workpiece S8 in the same manner as the arbor first described, and in the instance the arbor is pushed into the hole until the shoulder 56 engages the workpiece. In this manner, all workpieces are identically positioned on the arbor, and when the arbor is mounted in a checking machine or the like, all the workpieces are identically presented 4to the checking member of the machine. Manifestly, this arbor has the same advantages as the arbor first described in that it will fit any of a number of production parts which differ dimensionally within production tolerances. Further, it makes no difference insofar asthe operativeness of the arbor is concerned how the tolerances vary. For example, the arbor will t a workpiece 58 in which the hole portion 60 is `undersize and the hole portion 62 is oversize within permissible tolerances, as well as the workpiece in which the hole portion 60 is oversize and the hole portion 62 is undersize within permissible tolerances.

The form of the invention shown in FIG. 5 also is similar to the form of the invention shown in FIG. 1 except that modified externally threaded embossments 66 are provided and the arbor body itself is adapted for use as a permanent part of a checking machine or the like.

In the latter respect referred to above, one end of the arbor is made strong and rigid by a thick end wall 68 and the wall is provided with an axially extending shank 70. Only a fragmentary portion of the shank 70 is shown. It is contemplated that the shank 70 may be of any desired length and of any desired form. The primary purpose of the shank is to mount the arbor on a checking or other type machine and it will thus be apparent that the arbor may vary in both size and form depending upon the environment in which the arbor is adapted for use. It is intended that the arbor be suspended cantilever-fashion with the end 72 free so that the workpiece can be easily slipped onto the arbor from this end. Also, it will be observed that in this form of the invention the distal end 72 of the arbor is strengthened and made rigid by a relatively thick inturned flange 74. If desired, the ange 74 may be provided with a hole 76 having an outer bevel 78 adapted to receive a center or the like for supporting and steadying the otherwise unsupported end of the arbor.

When it is stated that the modified embossments 66 are externally threaded it is meant that the embossments are collectively threaded so that a workpiece 80 having an internally threaded hole 82 can be screwed onto the arbor as shown in the drawings. As in the forms of the invention first described, the embossments 66 are oversize with respect to the hole 82, and in this form of the invention suitable means preferably are provided for mechanically constructing or reducing the diameter of the arbor at the embossments prior to screwing the workpiece thereon. To this end, a flexible wire cable 84 or the like is wrapped around the arbor adjacent the embossment 66 and suitable means (not shown) are provided for selectively tightening and loosening the cable. For example, one end of the cable 84 can be anchored in any suitable manner and the other end attached to a manually operable lever or the like that can be manipulated to tension the cable. In Iany event, when the cable is tightened the flexible members 28 are simultaneously and uniformly arched inwardly to reduce the diameter of the arbor at the embossment 66. When the diameter of the arbor at the embossments is equal to or less than the diameter of the hole 32, the workpiece 80 can be easily screwed onto the arbor to the position shown in the drawings, and if the cable is then loosened inherent resiliency of the members 28 expand-s the arbor so that the external threads on the embossments 66 press solidly against the internal threads of the workpiece 80. However, since the arbor normally is larger in diameter at the embossments than the hole 82, the members 28 are arched inwardly, at least to some extent, even when the cable 84 is relaxed so that each embossment presses against the workpiece at longitudinally spaced points.

From the foregoing it will be readily apparent that this form of the invention functions in the same manner to achieve the same results as the forms first described. By reason of the pressure exerted by the arbor against the workpiece, the latter is chucked solidly on the pitch diameter of the thread. This makes it possible to perform a number of checking and machining operations on the work. For example, a workpiece chucked in the manner described can be easily checked to determine whether an end face of the workpiece is square with respect to the' axis of the hole or the pitch diameter of the thread. This operation is illustrated in the drawings wherein a conventional checking member 86 is shown in engagement with one end of the workpiece 80. When the arbor is rotated to turn the workpiece with respect to the checking member S6, it can be readily determined whether the end engaged by the member 86 is square with the rotational axis of the arbor and consequentially with the axis of the hole in which the arbor is mounted.

FIG. 6 shows still another modified arbor construction adapted to hold a workpiece solidly so that a machining or other operation can be performed thereon. In this connection it will be apparent that any machining operation exerts pressure on the workpiece which tends to move the latter either axially or rotatably on the arbor, and if the machine operation is to be performed successfully some means must be provided for preventing such relative movement.

Specifically, the arbor shown in FIG. 6 is generally similar to the form first described but the flexible members 28 are formed with modified embossments 88 which are adapted to accommodate a workpiece 90 having a relatively long hole or bore 92. lt will be observed that the embossments 8S are made correspondingly longer; and when the embossments are lengthened to the extent shown, they preferably are relieved in the middle, as at 94. Also, in this form of the invention the big end of the arbor is relatively thick-walled as at 96, and a sleeve 98 on and snugly fitting the portion 96 projects axially to provide a stop for the workpiece 90.

In order to lock the workpiece 90 on the arbor, the members 28 are formed substantially midway of the em bossments 88 with internal cam members 100 having cam surfaces 102 disposed concentrically around the axis of the arbor and tapered toward one end thereof. In the form of the invention shown, the cam surfaces 102 are tapered toward the end of the arbor which is adapted for insertion into the workpiece, and the relatively thick wall opposite end 96 of the arbor mounts means for applying pressure against the cam members. More specifically, a push shaft 104 is slidably mounted in the arbor and the shaft has a rounded end 106 which simultaneously engages the cam surfaces 102. An O-ring 108 supports the shaft 104 for free sliding movement in the arbor and also serves the function of sealing the operating parts of the chuck to the left of the ring as viewed in the drawings from dirt and grit that mayenter the arbor through the slots 26. A pressure screw 118 mounted in the arbor behind the shaft bears against the latter to press it solidly against the cam surfaces 162 so as to press the flexible members 28 solidly outwardly against the workpiece 90. The push shaft 104 preferably is formed with an enlarged head 112 having a spherically curved end surface 114 which seats against the inner end of the pressure screw 110 so as to reduce the area of engagement and consequentially the resistance to turning of the screw. Also, the bore of the arbor is enlarged to accommodate the head 112 and the enlarged portion of the bore defines a radial shoulder 116 which limits forward movement of' the shaft 104 and thus prevents inadvertent overstressing of the exible members 28. Any suitable means may be provided for rotating the pressure screw 118, and the latter is here shown provided with a socket 118 for receiving a conventional Allen wrench. A hardened ring 120 set into the arbor behind pressure screw 11G has a tapered outer surface 122 adapted to receive a suitable center 124. A` driver designated generally at 126 xed to the arbor body is used in the conventional manner to rotatively drive the arbor and the workpiece mounted thereon when the arbor is mounted between centers 124 and 128 as shown.

The pressure screw 116 normally is retracted to release the push shaft 104 so that the flexible members 28 function in the same manner as in the forms of the invention hereinabove described. The workpiece 90 can then be pushed onto the arbor to flex the members 28 inwardly as in the other forms of the invention. However, inasmuch as the inherent resiliency of the members 2S may not be sufficient to hold the workpiece stationary with respect to the arbor if a machining, grinding, or other operation is to be performed on the work, it is desirable, and in many instances necessary, to amplify the normal inherent holding power of the members. This is accomplished in the form of the invention here under consideration by tightening the pressure screw 110 against the push shaft 104 to force the latter solidly against the cam surfaces 102. Pressure exerted in this manner against the cam surfaces presses the members radially outwardly against the work and effectively locks the latter on the arbor. The arbor, with the workpiece mounted thereon, can then be placed between centers 124 and 128 as shown in the drawings and the arbor rotatively driven in the usual way to rotate the workpiece 99. The workpiece is held properly centered on the arbor and the end faces of the work can be machined exactly at right angles with respect to the axis of the hole in which the arbor is mounted. Also, it will be readily apparent that other operations can be easily performed on the workpiece in predetermined relation to the center of the hole 92.

Reference is now had to the form of the invention shown in FIG. 7 which illustrates a modified arbor construction adapted for internally splined workpieces. This form of the invention is similar to the form shown in FIG. 6 except that the flexible members 28 have cornparatively elongated embossments 13() provided with longitudinal splines 132 which are formed and spaced around the circumference of the arbor to interfit with the internal splines 134 of a workpiece 136. The instant device also has a modified driver comprising an elongated rod or pin provided with a longitudinally extending threaded stud 140 screwed into a correspondingly internally threaded hole 142 provided in the big end of the arbor. The driver 138 is more or less conventional in construction and functions in an obvious manner to rotatably drive the arbor when the latter is mounted for rotation on the centers 124 and 12S.

Also it will be observed that the arbor now under consideration is provided with a modified stop 144 which is particularly adapted and primarily intended for use with workpieces so formed that the radial face which engages the stop is not at right angles to the axis of the hole being chucked. It should be understood in this connection, however, that while the stop 144 is particularly adapted for the environment described, it is not limited thereto but can be used with any type workpiece, and it makes no difference whether the face of the workpiece engaged by the stop is at right angles or tapered with respect to the axis. Specifically, the stop 144 comprises a tubular sleeve 146 having a relatively narrow inturned flange 143 at the rearward end thereof which surrounds and is spaced from the portion 96 of the arbor. The sleeve 146 snugly fits and is held in coaxial relation with the arbor by a band of flexible material such as the O-ring 154) surrounding the arbor. The rearward end of sleeve 146 is formed with a flat taper, as at 152, and the forward end thereof is formed with a correspondingly flat taper 154. The two tapers 152 and 154 are disposed at right angles with respect to each other so that a double rocking action is provided for the stop 144. In the drawings, the ridge defined by the flat taper 152 extends horizontally of the arbor, and the ridge defined by the taper 154 extends vertically of the arbor. Thus the stop 146 has a line engagement with the workpiece 136, and the universal movement provided by the tapered ends 152 and 154 permits the stop to adapt itself readily to the workpiece.

It is obvious from the drawings that the arbor can be mechanically expanded against the workpiece 136 in the same manner as the arbor illustrated in FIG. 6 and that except for the differences noted above, the arbor functions in the same manner to achieve the same results as the arbor last described.

Reference is now had to FIGS. 8 and 9 which show an arbor adapted to be mechanically expanded and locked against the workpiece by a power actuator. More specifically, the arbor now under consideration is similar to the arbor illustrated in FIG. 6 and is equipped with a double rocking stop 144 similar to the one illustrated and described in connection with the form of the invention shown in FIG. 7. Also, in this form of the invention the big end of the arbor body fits snugly in an opening provided centrally in a fluid cylinder 162. A radial flange 164 on the arbor body is fastened securely to the cylinder 162 by screws 166. A power piston 168 is mounted for reciprocation in the cylinder 162 and the piston is normally retracted by springs in the cylinder ahead of the piston. In the particular environment shown in the drawing, the cylinder 162 is fastened to a rotatably driven spindle 172 of a machine tool (not shown) by screws 174. Fluid under pressure is supplied to the cylinder behind the piston in the usual manner from any suitable source through a pipe 176. According to the present invention, the power piston 168 replaces the pressure screws 110 shown in FIGS. 6 and 7, and to this end the head of the push shaft 104 is lengthened so that it extends into the cylinder 162 and butts against the hardened head of a pin 17S embedded centrally in the piston.

Initially in the operation of the arbor, fluid to the cylinder 162 is shut off so that the springs 170 retract the piston and permit the push shaft 104v to release the cams 160 so that the flexible members 128 assume their normal straight or rectilinear position. With the parts thus positioned, a workpiece can be readily slipped onto the arbor to engage the stop 144. Fluid under pressure is then `admitted to the cylinder 162 behind piston 168 to advance the latter against the push rod 104. The latter then advances against the cam 100 to expand the flexible members 2S against the workpiece so as to lock the arbor on the workpiece. In this connection, it will be observed that the head of pin 173 seats against the arbor body to limit forward travel of the piston 168 and to prevent overstressing of the arbor. In the drawings a cutting tool 182 is shown at the forward end of the workpiece 18) to illustrate a typical machining operation that can be performed on the workpiece when the latter is clamped in the manner described. lf desired, the distal end of the arbor can be supported by a tailstock center 128 as shown in the drawings.

What is claimed is:

An arbor comprising a tubular member of a diameter to loosely receive a workpiece to be chucked, embossments on one side of said tubular member and intermediate the ends thereof having peripheral work engaging surfaces, cams on the other side of said tubular member opposite said embossments, said tubular member having longitudinal slots extending through said embossments and said cams and terminating short of the ends of said tubular member and substantially equidistantly from opposite ends of said embossments, said slots defining flexible members having said embossments and said cams at substantially the middle thereof, the diameter of said arbor at said embossments providing and assuring an interference fit with a workpiece to be chucked thereby,

said embossments having beveled ends leading to said work engaging surfaces for guiding a workpiece onto said embossments, whereby a workpiece must be forced onto said work engaging surfaces when chucking and in so doing stresses said flexible members and said embossments into arcuate form with said flexible members and said work engaging surfaces arched in the same direction, each embossment in the stressed condition being at the bottom of and facing inwardly from the arch of its respective llexible member and having a concave work engaging surface engageable with the workpiece at axially spaced points to retain the workpiece without tilting and precisely coaxial to the member, said cams adapted to transmit pressure exerted there against in the direction of said embossments whereby to press the latter solidly against a workpiece disposed thereon, a cylinder fastened to the tubular member at one end thereof, a power piston mounted for reciprocation in said cylinder, and a pressure member confined between the piston and said cam members, said pressure member being movable against the cam surfaces of said cam members by said piston whereby to exert pressure on said cam surfaces tending to press said embossments against said workpiece and to augment pressure between said workpiece and said embossments at said spaced points.

No references cited. 

